User's Manual

Operating Your Computer 2-25
stations. GPS uses these "man-made stars" as reference points to calculate
positions accurate to a matter of meters. In fact, with advanced forms of
GPS you can make measurements to better than a centimeter! In a sense it
is like giving every square meter on the planet a unique address.
Here's how GPS works in five logical steps:
l The basis of GPS is "triangulation" from satellites.
l To "triangulate," a GPS receiver measures distance using the travel
time of radio signals.
l To measure travel time, GPS needs very accurate timing that it
achieves with some tricks.
l Along with distance, you need to know exactly where the satellites
are in space. High orbits and careful monitoring are the secret.
l Finally you must correct for any delays the signal experiences as it
travels through the atmosphere.
Five broad categories of GPS application:
l Location – determining a basic position
l Navigation – getting from one location to another
l Tracking – monitoring the movement of people and things
l Mapping – creating maps of the world
l Timing – bringing precise timing to the world